The invention relates to the healing of gaps in a film with a substance which can be deposited by photochemical methods.
The invention also relates to photovoltaic cells.
In one embodiment, the invention relates to the repair of defects in the amorphous silicon film layer of a photovoltaic cell.
A considerable amount of current research in the energy industry involves the conversion of the energy of the sun into usable electrical energy. It is known that crystalline materials such as silicon possess properties which enable the efficient conversion of sunlight to electrical energy. However, pure crystalline forms of silicon are extremely costly and are not feasible for most uses.
It is known that amorphous silicon- or germanium-containing films can be used in photovoltaic cells for the conversion of sunlight energy into electrical energy. Deposited amorphous silicon or germanium, however, is subject to the problem of microvoids and other defects such as pinholes, at which no material is deposited. In semiconductor cells having a metallic layer applied over the semiconducting layer, the pinhole can provide a site for the metal to contact the substrate, resulting in a localized electrical short and low conversion efficiency.
Methods for depositing an amorphous silicon film on a substrate have been developed to minimize the problem of pinhole defects. For example, glow discharge deposition is a method in which silane (SiH.sub.4) gas is passed through an evacuated reaction tube in which the silane is decomposed by a radio frequency glow discharge and deposited on a substrate at high substrate temperature. In another method of amorphous silicon deposition, called sputter deposition, an amorphous silicon film is deposited on a substrate in an argon and hydrogen atmosphere. It has been found that, because these methods leave localized film gaps, the resulting amorphous silicon film does not permit conversion of sunlight to electrical energy with sufficient efficiency to be economically feasible.
It is therefore an object of the present invention to provide an improved photovoltaic cell. It is a further object to provide a method for healing defects in amorphous semiconductor films.